Kappa opioid receptor activation induces epigenetic silencing of brain-derived neurotropic factor via HDAC5 in depression

Treatment-resistant depression (TRD) occurs in almost 50% of depressed patients. Central kappa opioid receptor (KOR) agonism has been demonstrated to induce depression and anxiety, while KOR antagonism alleviate depression like symptoms in rodent models and TRD in clinical studies. Previously, we have shown that sustained KOR activation leads to TRD-like phenotype in mice, and modulation of brain-derived neurotrophic factor (BDNF) expression in the prefrontal cortex (PFC) appears to be one of the molecular determinants of the antidepressant response. In the present study, we observed that sustained KOR activation by a selective agonist, U50488, selectively reduced the Bdnf transcripts II, IV , and Bdnf CDS (protein-coding Exon IX ) in the PFC and cultured primary cortical neurons, which was blocked by selective KOR antagonist, norbinaltorphimine. Considering the crucial role of epigenetic pathways in BDNF expression, we further investigated the role of various epigenetic markers in KOR induced BDNF downregulation in mice. We observed that treatment with U50488 resulted in selective and specific downregulation of acetylation at the 9th lysine residue of the histone H3 protein (H3K9ac) and upregulation of HDAC5 expression in the PFC. Further, using anti-H3K9ac and anti-HDAC5 antibodies in chromatin immune precipitation assay, we detected decreased enrichment of H3K9ac and increased HDAC5 binding at Bdnf II and IV transcripts after U50488 treatment, which were blocked by a selective KOR antagonist, norbinaltorphimine. Further mechanistic studies using HDAC5 selective inhibitor, LMK235, in primary cortical neurons, and adeno-associated viral shRNA mediated HDAC5-knockdown in the PFC of mice, we demonstrated an essential role of HDAC5 in KOR-mediated reduction of Bdnf expression in the PFC and depression-like symptoms in mice. These results suggest that KOR engages multiple pathways to induce depression-like symptoms in mice, and provide novel insights into the mechanisms by which activation of KOR regulates major depressive disorders. ### Competing Interest Statement The authors have declared no competing interest.